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. 2021 Sep 29;34(1):247–272. doi: 10.1093/plcell/koab237

Figure 3.

Figure 3

Design principles of different types of plant hormone sensors. A, DR5, an example of a plant hormone transcriptional sensor. The DR5 auxin synthetic promoter contains nine repeats (violet arrows) of ARF TF binding sites that control the expression of a FP in response to the hormone (green circle). B, qDII, an example of a plant hormone degradation-based sensor. The qDII ratiometric sensor is composed of two FPs: FP1, fused to a DII degron domain; and FP2, whose expression is controlled by the same constitutive promoter. Auxin triggers ubiquitination of the DII domain and the further degradation of FP1. This can be quantified using the FP2 signal, which remains constant, as a reference. C, D, FRET-based plant hormone sensors. Two types of FRET sensors are available. The auxin FRET sensor AuxSen (C) uses the dimer of TprR (Escherichia coli tryptophan repressor, in grey) fused to two FPs, the donor and acceptor, which come in close contact due to a conformational change that follows auxin binding to TprR. For ABACUS, ABAleon (ABA), and GPS1 (GA) FRET sensors (D), donor and acceptor FPs are fused to two protein interacting partners (light blue and yellow) that bind to each other in the presence of the hormone.